Methods and apparatus for antenna spoofing

ABSTRACT

In a method for utilizing beamforming in a wireless communication system, reference signals corresponding to a first communication channel from a first communication device to a second communication device are received, and an estimate of the first communication channel is generated using the received reference signals. One or more transmit beamforming vectors are calculated using the estimate of the first communication channel, and the one or more transmit beamforming vectors are utilized to transmit signals via a second communication channel from the second communication device to the first communication device while the first communication device assumes that the first second communication device is not utilizing beamforming.

CROSS-REFERENCES TO RELATED APPLICATIONS

This disclosure claims the benefit of U.S. Provisional PatentApplication No. 61/234,190, entitled “Antenna Spoofing Techniques forMIMO Systems,” filed on Aug. 14, 2009, which is hereby incorporated byreference herein in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication systems and,more particularly, to communication devices that utilize multipleantennas.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

In some communication systems, one or more communication devices employmultiple antennas. When a transmitter with multiple antennas does nothave information regarding a multiple-input, multiple-output (MIMO) ormultiple-input, single-output (MISO) channel between the transmitter anda receiver, the transmitter may employ transmit diversity. For example,a transmitter utilizes delay diversity by transmitting a signal via afirst transmitter and transmitting a time-delayed version of the signalvia a second transmitter. As another example, a transmitter utilizesdelay diversity by transmitting a signal via a first transmitter and atransmitting a frequency-offset version of the signal via a secondtransmitter. With antenna switching, a transmitter may choose a “best”antenna from a plurality of antennas, and then transmit using only thechosen antenna.

When a transmitter has MIMO or MISO channel information, the transmittermay develop a beamforming vector using the channel information to applycomplex-valued weights at each antenna to steer a beam towards thereceiver.

SUMMARY

In one embodiment, a method for utilizing beamforming in a wirelesscommunication system includes receiving reference signals correspondingto a first communication channel from a first communication device to asecond communication device, and generating an estimate of the firstcommunication channel using the received reference signals. The methodalso includes calculating one or more transmit beamforming vectors usingthe estimate of the first communication channel, and utilizing the oneor more transmit beamforming vectors to transmit signals via a secondcommunication channel from the second communication device to the firstcommunication device while the first communication device assumes thatthe first second communication device is not utilizing beamforming.

In another embodiment, an apparatus for utilizing beamforming in awireless communication system comprises a channel estimator to generatean estimate of a first communication channel from a first communicationdevice to a second communication device that includes the apparatus, thechannel estimator to generate the estimate of the first communicationchannel using reference signals received from the first communicationdevice via the first communication channel. The apparatus additionallycomprises a transmit beamforming calculator to calculate one or morebeamforming vectors based on an output of the channel estimator, and abeamforming unit to utilize the one or more transmit beamforming vectorson signals to be transmitted via a second communication channel from thesecond communication device to the first communication device. Also, theapparatus comprises a controller to cause the beamforming unit toutilize the one or more transmit beamforming vectors on signals to betransmitted via the second communication channel while the firstcommunication device assumes that the first second communication deviceis not utilizing beamforming.

In yet another embodiment, a method for utilizing beamforming in awireless communication system includes receiving reference signalscorresponding to a first communication channel from a firstcommunication device to a second communication device, and generating anestimate of the first communication channel using the received referencesignals. Additionally, the method includes calculating a plurality oftransmit beamforming vectors using the estimate of the firstcommunication channel, and utilizing each one of the plurality oftransmit beamforming vectors to transmit a respective sounding signalvia a second communication channel from the second communication deviceto the first communication device while the first communication deviceassumes that the first second communication device is utilizing arespective single antenna to transmit each sounding signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example wireless communication networkin which antenna spoofing techniques are utilized, according to anembodiment;

FIG. 2 is an example antenna spoofing method implemented by a userequipment communication device (UE), according to an embodiment;

FIG. 3 is an example method for calculating a transmit beamformingvector in the context of antenna spoofing, according to an embodiment;

FIG. 4 is another example antenna spoofing method implemented by a UE,according to another embodiment;

FIG. 5 is another example method for calculating a transmit beamformingvector in the context of antenna spoofing, according to anotherembodiment;

FIG. 6 is yet another example antenna spoofing method implemented by aUE, according to yet another embodiment; and

FIG. 7 is an example physical layer unit of a UE for implementingantenna spoofing, according to an embodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anevolved node base device (eNB) of a communication network transmits toand receives from one or more other wireless network devices, such as auser equipment device (UE). eNB and UE correspond to terminology used inthe 3^(rd) Generation Partnership Project Long Term Evolution (3GPP LTE)Standard. The apparatus and methods discussed herein, however, are notlimited to 3GPP LTE networks. Rather, the apparatus and methodsdiscussed herein may be utilized in other types of wirelesscommunication networks as well. For instance, another example systemthat may utilize embodiments of apparatus and methods described hereinis a technology promulgated by the Worldwide Interoperability forMicrowave Access (WiMAX) Forum (such systems conform to the Institutefor Electrical and Electronics Engineers (IEEE) 802.16e Standard). InWiMAX, a base station (BS) corresponds to the eNB of 3GPP LTE, and amobile station (MS) corresponds to the UE. In other embodiments, othertypes of systems utilize embodiments of apparatus and methods describedherein such as communication systems that conform to the IEEE 802.16Standard, wireless local area network (WLAN) systems such as systemsthat conform to the IEEE 802.11n Standard, etc. For ease of explanation,the description below refers to eNBs and UEs.

FIG. 1 is a block diagram of an example wireless communication network10, according to an embodiment. An eNB 14 includes a host processor 15coupled to a network interface 16. The network interface 16 includes amedium access control (MAC) unit 18 and a physical layer (PHY) unit 20.The PHY unit 20 includes a plurality of transceivers 21, and thetransceivers are coupled to a plurality of antennas 24. Although threetransceivers 21 and three antennas 24 are illustrated in FIG. 1, the eNB14 can include different numbers (e.g., 1, 2, 4, 5, etc.) oftransceivers 21 and antennas 24 in other embodiments. Also, in anotherembodiment, the eNB 14 includes more antennas 24 than transceivers 21,and includes an antenna switch (not shown) to couple the transceivers 21to different subsets of the antennas 24.

The network 10 includes a plurality of UEs 25. Although four UEs 25 areillustrated in FIG. 1, the network 10 can include different numbers(e.g., 1, 2, 3, 5, 6, etc.) of UEs 25 in various scenarios andembodiments. The UE 25-1 includes a host processor 26 coupled to anetwork interface 27. The network interface 27 includes a MAC unit 28and a PHY unit 29. The PHY unit 29 includes a plurality of transceivers30, and the transceivers 30 are coupled to a plurality of antennas 34.Although three transceivers 30 and three antennas 34 are illustrated inFIG. 1, the client station 25-1 can include different numbers (e.g., 1,2, 4, 5, etc.) of transceivers 30 and antennas 34 in other embodiments.Also, in another embodiment, the UE 25-1 includes more antennas 34 thantransceivers 30, and includes an antenna switch (not shown) to couplethe transceivers 30 to different subsets of the antennas 34.

In various embodiments, one or more of the UEs 25-2, 25-3, and 25-4 hasa structure the same as or similar to the client station 25-1.

In various embodiments, one or more of the PHY unit 20 and/or the MACunit 18 of the eNB 14, the PHY unit 29 and/or the MAC unit 28 of the UE25-1, and/or PHY units and/or MAC units of the other UEs 25 areconfigured to utilize “antenna spoofing” techniques described below. Forease of explanation, the UE 25-1 will be described below as utilizingantenna spoofing in communicating with the eNB 14. But in otherembodiments, the eNB 14 and/or other UEs 25 additionally oralternatively utilize antenna spoofing.

The term “antenna spoofing”, as used herein, generally refers totechniques in which a transmitter with multiple antennas utilizesbeamforming to transmit a signal to a receiver when the receiver assumesthat transmit beamforming is not being utilized. The receiver is“spoofed” in that, from the point of view of the receiver, thetransmitter appears to be transmitting from a single antenna, as oneexample, or is transmitting from multiple antennas using transmitdiversity but not beamforming, as another example. According to someembodiments, the transmitter utilizes knowledge of the reverse channel(i.e., the channel from the receiver to the transmitter) and channelreciprocity to determine a beamforming vector, in some embodiments.Several embodiments of antenna spoofing are described below.

As used herein, the term “transmitter” refers to the communicationdevice that performs antenna spoofing, and the term “receiver” refers tothe communication device to which the transmitter transmits signals.Thus, the “receiver” also typically is capable of transmission and the“transmitter” also typically is capable of reception, such as receivingsignals transmitted by the “receiver.” For example, in some embodimentsdiscussed below, the “receiver” transmits information to the“transmitter.”

System Model

An example model of a communication system in the context of antennaspoofing by a UE, according to an embodiment, will first be described.In the model, N_(t,UE) is the number of transmit (Tx) antennas at theUE. N_(s,UL) is the number of uplink (UL) streams, and N_(s,DL) is thenumber of downlink (DL) streams, where UL refers to transmissions fromthe UE to the eNB and DL refers to transmissions from the eNB to the UE.N_(t,eNB) is the number of Tx antennas at the eNB, and it is assumedthat the number of receive (Rx) antennas at the eNB is also N_(t,eNB),in one embodiment. As merely an example scenario provided forillustrative purposes, the current 3GPP LTE specification specifiesN_(s,UL)=1, a maximum of N_(s,DL) is 2, and assumes N_(t,UE) is 2 for ULantenna selection. In other scenarios, N_(s,UL), N_(s,DL), and N_(t,UE)have other suitable values.

In the example model, reciprocity between the UL channel and the DLchannel is assumed. If the UL MIMO channel is H_(u) (anN_(t,eNB)×N_(t,UE) matrix) and the DL MIMO channel is H_(d) (anN_(t,UE)×N_(t,eNB) matrix), then channel reciprocity can be representedas H_(u)=H_(d) T. Communication channels such as mobile communicationare time-varying, and uplink and downlink transmissions may occur atdifferent times, such as with a time-division duplex (TDD) system.Therefore, for reciprocity to hold, the channel generally should berelatively slowly time-varying. The time over which a channel remainsrelatively constant is sometimes referred to as the coherence time. Thecoherence time is sometimes defined as the delay δt at which a squaredmagnitude of an autocorrelation of the impulse response h(t) of thechannel drops below a certain fraction (often ½) of the autocorrelationat zero delay. To use DL channel measurements made at time t to estimatethe UL channel a t+Δ, then Δ should be shorter than the coherence timeto ensure a certain level of performance.

Additionally, for reciprocity to hold, the frequencies at which the ULchannel and the DL channel operate should be the overlapping or thechannels must be frequency invariant over a range of frequenciesspanning both the UL and DL channels.

In transceivers having multiple transmit and receive chains, theresponses of the individual transmit chains and receive chains may causea reciprocal channel to violate reciprocity when considering a compositechannel that includes the responses of the transmit and receive chainsof the UE and the eNB. Thus, calibration that takes into account theresponses of the individual transmit chains and receive chains isutilized, in some embodiments and/or scenarios.

A singular value decomposition (SVD) of the MIMO UL channel isH _(u) =UΛV*  Equ. 1where U and V are unitary matrices, Λ is a diagonal matrix with elementsλ₁≧ . . . ≧λ_(N) _(t,UE) , and * denotes the conjugate transposeoperation. Additionally, V has column vectors v₁, . . . , v_(N) _(t,UE), corresponding λ₁≧ . . . ≧λ_(N) _(t,UE) , Further, it is assumed thatN _(t,UE) ≦N _(t,eNB)  Equ. 2i.e., that the number of antennas at the eNB is the same as or greaterthan the number of antennas at the UE. The SVD of the MIMO DL channelis:H _(d) =V* ^(T) ΛU ^(T)  Equ. 3

The above-discussed system model is in the context of 3GPP LTE networks.Similar system models for other types of networks such as WiMAXnetworks, WLAN networks that conform to the IEEE 802.11n Standard, etc.,will be apparent to those of ordinary skill in the art in light of thepresent disclosure and teachings herein.

Antenna Spoofing

Several example methods of antenna spoofing will now be described. Theseexample methods are in the context of a UE utilizing beamforming totransmit to an eNB. In other embodiments, however, similar methods arein the context of an eNB utilizing beamforming to transmit to a UE.Additionally, the use of the terms eNB and UE is merely for explanatorypurposes and does not limit these methods to 3GPP LTE implementations.These techniques can be utilized in other types of wirelesscommunication networks as well, such as WiMAX networks, WLAN networksthat conform to the IEEE 802.11n Standard, etc.

Generally, the example antenna spoofing methods involve the UE utilizingone or more beamforming vectors p_(i) to transmit to the eNB when theeNB expects that the UE is not using beamforming, where i is an indexindicating an uplink stream or a sounding signal transmission from a Txparticular antenna, for example. As one example of when the eNB expectsthat the UE is not using beamforming, the eNB expects that the UEtransmits each sounding signal from a single antenna, i.e., the eNB doesnot expect that the UE uses beamforming to transmit a sounding signal.

FIG. 2 is an example antenna spoofing method 100 implemented by a UE,according to an embodiment. The method 100 is utilized by the UE totransmit signals to the eNB using beamforming when the eNB does notexpect that the UE is using beamforming, in an embodiment. For example,the eNB assumes the UE is transmitting using a single antenna (e.g.,antenna switching) or is transmitting using a diversity technique thatdoes not utilize knowledge of the UL channel or the DL channel, such asdelay diversity or frequency offset diversity. In some embodiments, theeNB does not expect that the UE is using beamforming because the eNB hasnot provided the UE with channel information feedback regarding the ULchannel such as channel condition information, signal-to-noise ratio(SNR) information, codebook selection information, etc. According to oneembodiment of the method 100, it is assumed thatN_(t,UE)≧N_(c)>N_(s,UL), where N_(c) is the number of Tx chains at theUE.

At block 104, the UE receives reference signals from the eNB, such assounding signals, pilot signals, etc. At block 108, the UE estimates theDL channel H_(d) based on the reference signals received at block 104.

At block 112, the UE exploits channel reciprocity between UL and DL tocalculate one or more transmit beamforming vectors using the DL channelestimate H_(d). Any suitable technique for calculating the one or moretransmit beamforming vectors using the DL channel estimate H_(d) isutilized. One example technique for implementing block 112 is describedwith reference to FIG. 3. In one embodiment, the UE calculates N_(s,UL)beamforming vectors p_(i) for i=1, . . . , N_(s,UL).

At block 116, the UE utilizes the one or more beamforming vectors totransmit data to the eNB via the UL channel when the eNB does not expectthat the UE is using beamforming. In one embodiment, the UE utilizesrespective beamforming vectors p_(i), for i=1, . . . , N_(s,UL), totransmit the N_(s,UL) UL streams. In one embodiment, the UE utilizes theone or more beamforming vectors to transmit a single stream to the eNBvia the UL channel when the eNB assumes the UE is transmitting using asingle antenna (e.g., antenna switching). In another embodiment, the UEutilizes the one or more beamforming vectors to transmit a single streamto the eNB via the UL channel when the eNB assumes the UE istransmitting using multiple antennas using a diversity technique thatdoes not utilize knowledge of the UL channel or the DL channel, such asdelay diversity or frequency offset diversity. In yet anotherembodiment, the UE utilizes the one or more beamforming vectors totransmit multiple streams simultaneously to the eNB via the UL channelwhen the eNB does not expect that the UE is using beamforming.

In some embodiments or scenarios, the method 100 achieves greater ULthroughput at compared to UL antenna switching or UL diversitytechniques that do not utilize knowledge of the UL channel or the DLchannel.

FIG. 3 is an example method 150 for implementing block 112 of FIG. 2,according to an embodiment. The method 150 exploits channel reciprocitybetween UL and DL to estimate the UL channel H_(u), and to use H_(u) tocalculate the one or more beamforming vectors.

At block 154, channel reciprocity is utilized to determine H, fromH_(d). For example, in one embodiment, the UL channel is estimated asH_(u)=H_(d) ^(T). In some embodiments, calibration is also utilized toestimate H_(u).

At block 158, the SVD of H_(u) is calculated. If N_(t,UE)>N_(c), foreach set of N_(c) antennas, an SVD of the channel estimate H_(u) for theset is calculated, and a suitable metric of the λ_(i)'s is calculated.Example metrics include a summation of the λ_(i)'s, an average of theλ_(i)'s, a weighted average of the λ_(i)'s, etc. Then, a set of antennascorresponding to the best (e.g., largest) metric is selected, and theSVD corresponding to the selected set is noted.

At block 162, the one or more beamforming vectors are determined usingthe SVD determined at block 158. If N_(t,UE)>N_(c), the SVD that is usedis the SVD corresponding to the set of antennas having the best (e.g.,largest) metric. The block 162 includes determining the one or morebeamforming vectors p_(i) as the first N_(s,UL) column vectors of V,i.e., p_(i)=v_(i) for i=1, . . . , N_(s,UL), according to oneembodiment.

FIG. 4 is another example antenna spoofing method 200 implemented by aUE, according to another embodiment. The method 200 is utilized by theUE to select a beamforming vector by using an antenna selectionprocedure implemented with the eNB. The eNB does not expect that the UEis using beamforming because the eNB assumes that the UE is transmittingeach sounding signal using a single antenna. According to one embodimentof the method 200, it is assumed that N_(t,UE)≧N_(c)>N_(o)≧N_(s,UL),where N_(o) is the number of sounding opportunities, where a soundingopportunity is an available time slot in which the UE can send trainingsignals from a transmit antenna, in an embodiment. For example, the eNBassigns N_(o) time slots in which the UE can send sounding signals. In atypical antenna switching procedure, the UE sends a sounding signal viaa respective antenna in each assigned sounding time slot.

At block 204, the UE receives reference signals from the eNB, such assounding signals, pilot signals, etc. At block 208, the UE estimates theDL channel H_(d) based on the reference signals received at block 204.

At block 212, the UE exploits channel reciprocity between UL and DL tocalculate one or more transmit beamforming vectors using the DL channelestimate H_(d). Any suitable technique for calculating the one or moretransmit beamforming vectors using the DL channel estimate H_(d) isutilized. In some embodiments, block 212 includes calculating the SVD ofH_(u). In these embodiments, if N_(t,UE)>N_(c), for each set of N_(c)antennas, an SVD of the channel estimate H_(u) for the set iscalculated, and a suitable metric of the λ_(i)'s is calculated. Examplemetrics include a summation of the λ_(i)'s, an average of the λ_(i)'s, aweighted average of the λ_(i)'s, etc. Then, a set of antennascorresponding to the best (e.g., largest) metric is selected, and theSVD corresponding to the selected set is noted.

In one embodiment, the UE calculates N_(o) beamforming vectors p_(i). Inembodiments in which the SVD of H_(u) is calculated, N_(s,UL)beamforming vectors p_(i) for i=1, . . . , N_(s,UL), are set to v_(i).In one embodiment, p_(i)=wv_(i-N) _(s,UL) +(1−w)v_(i) for i=N_(s,UL)+1,. . . , N_(o), where 0≦w≦1. The parameter w indicates a confidence levelof channel knowledge, for example. As the confidence level goes up, wapproaches 1, at which beamforming vectors for i=N_(s,UL)+1, . . . ,N_(o) are redundant.

At block 216, the UE transmits UL sounding signals to the eNB usingrespective beamforming vectors during time periods in which the eNBexpects the UE to transmit the sounding signals using antenna switching,i.e., using respective single antennas. In one embodiment, the UEutilizes respective beamforming vectors p_(i), for i=1, . . . , N_(o),to transmit the respective UL sounding signals.

Upon receiving the N_(o) sounding signals, the eNB assumes that eachsounding signal was transmitted via a respective single antenna at theUE. The eNB then determines which sounding signal has the “best”characteristics, e.g., highest SNR, and transmits to the UE anindication of the “antenna” that corresponds to the “best”characteristics.

At block 220, the UE receives from the eNB the indication of the“antenna” chosen by the eNB and that corresponds to the “best”characteristics. At block 224, the UE utilizes the indication receivedat block 220 to select a beamforming vector p_(i). At block 228, the UEutilizes the beamforming vector selected at block 224 to transmit ULsignals.

In some embodiments or scenarios, the method 200 achieves greater ULthroughput as compared to traditional antenna switching, whileprocessing at the eNB is the same as compared to antenna switching.

FIG. 5 is an example method 250 for implementing block 212 of FIG. 4,according to an embodiment. The method 250 exploits channel reciprocitybetween UL and DL to estimate the UL channel H_(u), and to use H_(u) tocalculate the one or more beamforming vectors.

At block 254, channel reciprocity is utilized to determine H_(u) fromH_(d).

For example, in one embodiment, the UL channel is estimated asH_(u)=H_(d) ^(T). In some embodiments, calibration is also utilized toestimate H_(u).

At block 258, the SVD of H_(u) is calculated. If N_(t,UE)>N_(c), foreach set of N_(c) antennas, an SVD of the channel estimate H_(u) for theset is calculated, and a suitable metric of the λ_(i)'s is calculated.Example metrics include a summation of the λ_(i)'s, an average of theλ_(i)'s, a weighted average of the λ_(i)'s, etc. Then, a set of antennascorresponding to the best (e.g., largest) metric is selected, and theSVD corresponding to the selected set is noted.

At block 262, N_(o) beamforming vectors are determined using the SVDdetermined at block 258. N_(s,UL) beamforming vectors p_(i) for i=1, . .. , N_(s,UL), are set to v_(i). In one embodiment, p_(i)=wv_(i-N)_(s,UL) +(1−w)v_(i), for i=N_(s,UL)+1, . . . , N_(o), where 0≦w≦1.

FIG. 6 is yet another example antenna spoofing method 300 implemented bya UE, according to yet another embodiment. The method 300 is utilized bythe UE to influence the selection of a beamforming vector by the eNB forDL transmissions to the UE. The method 300 exploits UL sounding forpurposes of DL beamforming. The eNB does not expect that the UE is usingbeamforming because the eNB assumes that the UE is transmitting eachsounding signal using a single antenna. According to one embodiment ofthe method 300, it is assumed thatN _(t,UE) ≧N _(c) >N _(o) ≧N _(s,UL).

At block 304, the UE receives reference signals from the eNB, such assounding signals, pilot signals, etc. At block 308, the UE estimates theDL channel H_(d) based on the reference signals received at block 304.

At block 312, the UE exploits channel reciprocity between UL and DL tocalculate one or more transmit beamforming vectors using the DL channelestimate H_(d). Any suitable technique for calculating the one or moretransmit beamforming vectors using the DL channel estimate H_(d) isutilized. In some embodiments, block 312 includes calculating the SVD ofH_(u). In these embodiments, if N_(t,UE)>N_(c), for each set of N_(c)antennas, an SVD of the channel estimate H_(u) for the set iscalculated, and a suitable metric of the λ_(i)'s is calculated. Examplemetrics include a summation of the λ_(i)'s, an average of the λ_(i)'s, aweighted average of the λ_(i)'s, etc. Then, a set of antennascorresponding to the best (e.g., largest) metric is selected, and theSVD corresponding to the selected set is noted.

In one embodiment, the UE calculates N_(o) beamforming vectors p_(i). Inembodiments in which the SVD of H_(u) is calculated, N_(s,UL)beamforming vectors p_(i) for i=1, . . . , N_(s,UL), are set to v_(i).In one embodiment, p_(i)=wv_(i-N) _(s,UL) +(1−w)v_(i) for i=N_(s,UL)+1,. . . , N_(o), where 0≦w≦1. The parameter w indicates a confidence levelof channel knowledge, for example. As the confidence level goes up, wapproaches 1, at which beamforming vectors for i=N_(s,UL)+1, . . . ,N_(o) are redundant.

In one embodiment, block 312 comprises the method 250 of FIG. 5.

At block 316, the UE transmits UL sounding signals to the eNB usingrespective beamforming vectors during time periods in which the eNBexpects the UE to transmit the sounding signals using antenna switching,i.e., using respective single antennas. In one embodiment, the UEutilizes respective beamforming vectors p_(i), for i=1, . . . , N_(o),to transmit the respective UL sounding signals.

Upon receiving the N_(o) sounding signals, the eNB assumes that eachsounding signal was transmitted via a respective single antenna at theUE. In other words, the eNB assumes that it has received each soundingsignal via H_(u)e_(i), where e_(i) is a vector with the i-th componentset to one and all other components set to zero. The eNB has in fact,however, received each sounding signal via H_(u)p_(i). Thus, the eNBestimates the UL channel as H_(u)′=H_(u)P, where P is a matrix havingthe N_(o)p_(i) column vectors. Next the eNB exploits reciprocity andestimates the DL channel as H_(d)′=(H_(u)P)^(T)=P^(T)H_(d). Then, theeNB uses H_(d)′ to calculate one or more beamforming vectors. Forexample, the eNB utilizes the SVD of H_(d)′ to determine one or morebeamforming vectors in a manner similar to the techniques describedabove, in one embodiment. As another example, the eNB utilizes theTomlinson-Harashima precoding technique, in another embodiment. In anycase, the eNB assumes that it is using H_(u) as opposed to H_(u)′.

At block 320, the UE receives from the eNB beamformed DL signals,wherein the DL signals are beamformed using the one or more beamformingvectors calculated by the eNB using H_(u)P.

In some embodiments or scenarios, the method 300 achieves the samebeamforming and/or performance as when the eNB has full knowledge ofH_(d). For example, in some embodiments or scenarios compared with afull sounding technique, the method 300 achieves the same performancewith less overhead, i.e., less UL sounding transmissions. Also, in someembodiments or scenarios, compared with antenna-by-antenna sounding, themethod 300 achieves better performance with the same number of soundingtransmissions.

FIG. 7 is a block diagram of an example PHY unit 400 for a UE thatimplements one or more of the example methods of FIGS. 2-6, according toan embodiment. The PHY unit 400 includes a signal processor 404 thatreceives bits for transmission via the UL channel and performs variousoperations such as one or more of encoding, interleaving, streamparsing, mapping to bits to symbols, etc. Multiple outputs of the signalprocessor 404 are provided to a beamforming unit 408 that utilizes abeamforming network to apply a beamforming vector to signals to betransmitted via the UL channel. A plurality of Tx chains 412 upconvertthe beamformed signals to radio frequency (RF) for transmission. Anantenna switch 416 switches the outputs of the Tx chains 412 between alarger number of antennas 420.

Similarly, the antenna switch 416 switches the antennas 420 between asmaller number of receive (Rx) chains 424. The Rx chains 424 downcovertDL signals from RF. If Rx beamforming is utilized, the beamformer 408applies Rx beamforming to the outputs of the Rx chains 424. The signalprocessor 404 performs operations on outputs of the beamforming unit 408corresponding to DL signals, such as symbol detection, mapping symbolsto bits, decoding, etc., to generate a DL bit stream. If the number ofantennas 420 is the same as the number of Tx chains and the number of Rxchains, the antenna switch 416 is omitted, in some embodiments.

A channel estimator 428 is coupled to the signal processor 404. Thechannel estimator 428 is configured to generate an estimate of the DLchannel H_(d) based on reference signals received from the eNB via theDL channel. Additionally, the channel estimator 428 is configured toutilize channel reciprocity to determine H_(u) from H_(d). For example,in one embodiment, the channel estimator 428 is configured to estimateH_(u) as H_(d) ^(T). In some embodiments, the channel estimator 428 alsoutilizes calibration to estimate H_(u) based on H_(d).

A beamforming vector calculator 432 is coupled to the channel estimator428 and the beamforming unit 408. The beamforming vector calculator 432is configured to calculate beamforming vectors based on H_(u), and tosupply the beamforming vectors to the beamforming unit 408. A controller436 is coupled to the antenna switch 416 and the beamforming vectorcalculator 432. The controller 436 is configured to control whichantennas 420 are used for a particular transmission, and to controlwhich beamforming vector is supplied to the beamforming unit 408 for aparticular transmission.

In one embodiment, the PHY unit 400 is configured to implement themethod 100 of FIG. 2. For example, the channel estimator 428 estimatesH_(d) based on DL reference signals received by the PHY unit 400. Also,the channel estimator 428 and the beamforming vector calculator 432calculate one or more beamforming vectors using an estimate of H_(d).The controller 436 causes the beamforming vector calculator 432 tosupply the calculated beamforming vector(s) to the beamforming unit 408,which uses the beamforming vector(s) to beamform during transmission ofUL signals.

In one embodiment, the PHY unit 400 is configured to implement themethod 150 of FIG. 3. For example, the channel estimator 428 determinesH_(u) from H_(d). The beamforming vector calculator 432 calculates SVDof H_(u). The beamforming vector calculator 432 calculates one or morebeamforming vectors using the SVD.

Similarly, the PHY unit 400 is configured to implement the method 200 ofFIG. 4, in one embodiment. For example, the controller 436 causes thePHY unit 400 to transmit UL sounding signals using respectivebeamforming vectors calculated by the channel estimator 428 and thebeamforming vector calculator 432. Also, the controller 436 receives theindication from the eNB (block 220) and uses the indication to controlthe beamforming vector calculator 432 to provide the appropriatebeamforming vector to the beamforming unit 408 for transmission of ULsignals.

In a similar manner, the PHY unit 400 is configured to implement themethods of FIGS. 5 and 6.

In other embodiments, the PHY unit 29 (FIG. 1) is configured toimplement one or more of the methods of FIGS. 2-6.

In other embodiments, methods similar to those discussed above areimplemented by the eNB. In these embodiments, the PHY unit 20 (FIG. 1)is configured to implement one or more of the methods. Additionally, inone embodiment, the PHY unit 20 has a structure similar to the PHY unitof FIG. 7.

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. Likewise, the software or firmware instructionsmay be delivered to a user or a system via any known or desired deliverymethod including, for example, on a computer readable disk or othertransportable computer storage mechanism or via communication media.Communication media typically embodies computer readable instructions,data structures, program modules or other data in a modulated datasignal such as a carrier wave or other transport mechanism. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, radio frequency,infrared and other wireless media. Thus, the software or firmwareinstructions may be delivered to a user or a system via a communicationchannel such as a telephone line, a DSL line, a cable television line, afiber optics line, a wireless communication channel, the Internet, etc.(which are viewed as being the same as or interchangeable with providingsuch software via a transportable storage medium). The software orfirmware instructions may include machine readable instructions that,when executed by the processor, cause the processor to perform variousacts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe invention.

What is claimed is:
 1. A method for utilizing beamforming in a wirelesscommunication system, the method comprising: receiving reference signalsvia a first communication channel from a first communication device to asecond communication device; generating an estimate of the firstcommunication channel using the received reference signals; calculatingone or more transmit beamforming vectors using the estimate of the firstcommunication channel; and utilizing the one or more transmitbeamforming vectors to transmit signals via a second communicationchannel from the second communication device to the first communicationdevice, wherein the first communication device processes the signalstransmitted from the second communication device to the firstcommunication device according to a model H e_(i), where H is a matrixrepresenting the second communication channel, and where e_(i) is avector with all components of e_(i), except an i^(th) component ofe_(i), being equal to zero.
 2. A method according to claim 1, whereinthe estimate of the first communication channel is an estimatecorresponding to a set of receive antennas; wherein the method furthercomprises: generating other estimates of the first communication channelcorresponding to other sets of receive antennas; and selecting one ofthe estimates for calculation of the one or more transmit beamformingvectors.
 3. A method according to claim 1, wherein calculating the oneor more transmit beamforming vectors using the estimate of the firstcommunication channel comprises: determining an estimate of the secondcommunication channel using the estimate of the first communicationchannel; and calculating the one or more transmit beamforming vectorsusing the estimate of the second communication channel.
 4. A methodaccording to claim 3, wherein calculating the one or more transmitbeamforming vectors using the estimate of the second communicationchannel comprises: calculating a singular value decomposition (SVD) of amatrix corresponding to the estimate of the second communicationchannel; and determining the one or more transmit beamforming vectorsusing the SVD.
 5. A method according to claim 4, wherein determining theone or more transmit beamforming vectors using the SVD comprisesdetermining the one or more transmit beamforming vectors using vectorsfrom a V matrix from the SVD.
 6. A method according to claim 1, whereinutilizing the one or more transmit beamforming vectors comprisesutilizing the one or more transmit beamforming vectors to transmit aplurality of streams simultaneously.
 7. An apparatus for utilizingbeamforming in a wireless communication system, the apparatuscomprising: a channel estimator to generate an estimate of a firstcommunication channel from a first communication device to a secondcommunication device that includes the apparatus, the channel estimatorto generate the estimate of the first communication channel usingreference signals received from the first communication device via thefirst communication channel; a transmit beamforming calculator tocalculate one or more beamforming vectors based on an output of thechannel estimator; a beamforming unit to utilize the one or moretransmit beamforming vectors on signals to be transmitted via a secondcommunication channel from the second communication device to the firstcommunication device; and a controller to cause the beamforming unit toutilize the one or more transmit beamforming vectors on signals to betransmitted via the second communication channel, wherein the firstcommunication device processes the signals transmitted from the secondcommunication device to the first communication device according to amodel H e_(i), where H is a matrix representing the second communicationchannel, and where e_(i) is a vector with all components of e_(i),except an i^(th) component of e_(i), being equal to zero.
 8. Anapparatus according to claim 7, wherein the channel estimator isconfigured to generate a plurality of estimates of the firstcommunication channel using different sets of receive antennas and toselect one of the estimates for calculation of the one or more transmitbeamforming vectors.
 9. An apparatus according to claim 7, wherein thechannel estimator is configured to determine an estimate of the secondcommunication channel using the estimate of the first communicationchannel; and wherein the transmit beamforming calculator is configuredto calculate the one or more beamforming vectors based on the estimateof the second communication channel.
 10. An apparatus according to claim9, wherein the transmit beamforming calculator is configured to:calculate a singular value decomposition (SVD) of a matrix correspondingto the estimate of the second communication channel, and determine theone or more transmit beamforming vectors using the SVD.
 11. An apparatusaccording to claim 10, wherein the transmit beamforming calculator isconfigured to determine the one or more transmit beamforming vectorsusing vectors from a V matrix from the SVD.
 12. An apparatus accordingto claim 7, wherein the controller is configured to cause thebeamforming unit to utilize a plurality of transmit beamforming vectorsto transmit a plurality of sounding signals via the second communicationchannel.
 13. An apparatus according to claim 12, wherein the controlleris configured to: select one of the plurality of transmit beamformingvectors based on an indication received from the first communicationdevice, the indication corresponding to one of the plurality of soundingsignals, and cause the beamforming unit to utilize the selected transmitbeamforming vector to transmit signals via the second communicationchannel.
 14. A method for utilizing beamforming in a wirelesscommunication system, the method comprising: receiving reference signalsvia a first communication channel from a first communication device to asecond communication device; generating an estimate of the firstcommunication channel using the received reference signals; calculatinga plurality of transmit beamforming vectors using the estimate of thefirst communication channel; utilizing each one of the plurality oftransmit beamforming vectors to transmit a respective sounding signalvia a second communication channel from the second communication deviceto the first communication device; receiving an antenna indication fromthe first communication device, wherein the antenna indicationcorresponds to one of the sounding signals; selecting, based on theantenna indication, one of the plurality of transmit beamformingvectors; and utilizing the selected transmit beamforming vector totransmit signals via the second communication channel.
 15. A methodaccording to claim 14, wherein the estimate of the first communicationchannel is an estimate corresponding to a set of receive antennas;wherein the method further comprises: generating other estimates of thefirst communication channel corresponding to other sets of receiveantennas; and selecting one of the estimates for calculation of theplurality of transmit beamforming vectors.
 16. A method according toclaim 14, wherein calculating the one or more transmit beamformingvectors using the estimate of the first communication channel comprises:determining an estimate of the second communication channel using theestimate of the first communication channel; and calculating theplurality of transmit beamforming vectors using the estimate of thesecond communication channel.
 17. A method according to claim 16,wherein calculating the plurality of transmit beamforming vectors usingthe estimate of the second communication channel comprises: calculatinga singular value decomposition (SVD) of a matrix corresponding to theestimate of the second communication channel; and determining theplurality of transmit beamforming vectors using the SVD.
 18. A methodaccording to claim 17, wherein determining the one or more transmitbeamforming vectors using the SVD comprises determining the one or moretransmit beamforming vectors using vectors from a V matrix from the SVD.